Vehicle detecting apparatuses have been used to acquire traffic information or use in of a parking lot. As these vehicle detecting apparatuses, a loop type vehicle detecting apparatus for detecting a vehicle behavior parked state, a stopped state, a passing state of a vehicle, or the like) by using variations in inductance of a loop coil that is mounted in a detecting area (a parked area, a stopped area, or a passing area of a vehicle) has been proposed.
FIG. 3 is a functional block diagram of a low power operated loop type vehicle detecting apparatus in accordance with the related art.
As shown in FIG. 3, the loop type vehicle detecting apparatus in accordance with the related art is configured to include a resonance oscillation circuit unit 110 that includes an LC resonator 111 including a loop coil 111a mounted in a detecting area and an oscillator 112 connected with the LC resonator 111 and a vehicle behavior determination unit 120 connected with the resonance oscillation circuit unit 110.
The loop coil 111a is connected with a protective circuit (not shown) for preventing overcurrent due to lightning from flowing into the resonance oscillation circuit unit 110.
The LC resonator 111 is resonated with a resonance frequency that varies with a change in an inductance, value of the loop coil 111a. The inductance value of the loop coil 111a is reduced when metal components of a vehicle electromagnetically interact with the loop coil 111a. As a result, when a vehicle accesses the loop coil 111a, the resonance frequency of the LC resonator 111 is increased.
The LC resonator 111 having the above configuration may include frequency selective characteristics by impedance matching.
The oscillator 112 is oscillated with a frequency that varies with the change in the resonance frequency of the LC resonator 111.
The oscillator 112 is continuously applied with operating voltage.
A frequency of an analog oscillator signal that is output from the oscillator 112 is increased when the vehicle accesses the loop coil 111a (when the vehicle accesses the loop coil, the resonance frequency of the LC resonator is increased).
The vehicle behavior determination unit 120 is configured to include an analog-digital converter 121 that converts an analog oscillation signal output from the resonance oscillation circuit unit 110 into a digital oscillation signal of the same frequency, an oscillation clock counter 127 that counts a clock of the digital oscillation signal converted in the analog-digital converter 121, and a vehicle behavioral state determiner 125 that determines a vehicle behavioral state based on the number of digital oscillation signal clocks counted in the oscillation clock counter 127.
The vehicle behavioral state determiner 125 determines a vehicle behavioral state by calculating the frequency by dividing the number of digital oscillation signal clocks counted in the oscillation clock counter 127 by a predetermined time (usually, 10 to 100 msec) and comparing the calculated frequency with the preset number of vehicle behavior reference clocks stored in a memory.
However, according to the low power operated loop type vehicle detecting apparatus, the operating voltage is continuously applied to the oscillator 112, which may lead to the increase in power consumption.
As such, when the power consumption is increased, a secondary problem of frequently replacing a voltage source occurs.